Repeatable optical waveguide interconnection including an index matching elastomeric solid layer providing core and cladding index of refraction matching and related methods

ABSTRACT

A repeatable optical waveguide interconnection may include first and second optical waveguides having respective first and second end faces. Each of the first and second optical waveguides may include a core having a core index of refraction, and a cladding surrounding the core and having a cladding index of refraction different than the core index of refraction. The interconnection may further include a first index matching elastomeric solid layer having a proximal face coupled to the first end face, and a distal face opposite the proximal face to be repeatably optically coupled to the second end face. The first index matching elastomeric solid layer may have an index of refraction profile matching an index of refraction of the core and the cladding.

FIELD OF THE INVENTION

The present invention relates to the field of optical waveguides andoptical fibers, and, more particularly, to optical fiber connectors,waveguide devices, and related methods.

BACKGROUND OF THE INVENTION

Optical fibers are commonly used in telecommunications for communicatingdata signals over both short and long distances. With respect to othercommunication mediums, such as metal wires, optical fibers areadvantageous in that signals travel along them with less loss, and theyare also less susceptible to electromagnetic interference. Opticalfibers also enjoy very high bandwidth (i.e., data rates). Optical fibersmay also be used for illumination, and may be wrapped in bundles andused to carry images, such as in fiber optic cameras. Optical fibers mayalso be used in other applications, such as sensors and lasers, forexample.

One disadvantage of optical fibers, however, is that they are moredifficult to couple together than wire conductors, as discontinuities ata connection point can lead to light reflection and losses thatsignificantly degrade signal quality. One approach to joining opticalfibers is the use of mechanical fusion splicers, which align and fusetwo fiber ends together. While this provides a very low loss connectionbetween the fibers, fusion couplers are typically very expensive, andthus not practical for many implementations. Fusion splicers formpermanent connections and are less suitable for temporary splices orother connections that are to be made temporary or dynamic.

Another approach used in some optical interfaces is to apply anindex-matched material, such as liquids or gels. While such materialsmay generally be formulated to match the index of refraction of anoptical medium, problems may arise due to migration of the index-matchedmaterial and contamination in unwanted areas. Moreover, such materialsare prone to attract dirt, and are typically difficult to clean oncecontaminated.

U.S. Pat. No. 5,778,127 to Gilliand et al. discloses an opticaltransceiver apparatus which has a housing including a diode packagealigned with a lens, and having an optical filler composition injectedtherebetween. The optical filler composition comprises a siliconeelastomer which may be used as an index matching element, as apositioning and locking means, or an optical attenuator. Other exemplaryapproaches for optical fiber connectors or terminations are set forth inthe following references: U.S. Pat. No. 5,619,610 to King et al.; U.S.Pat. No. 5,515,465 to Olin et al.; U.S. Pat. No. 6,501,900 to Aloisio,Jr. et al.; U.S. Pat. No. 6,097,873 to Filas et al.; and U.S. Pat. No.5,058,983 to Corke et al.

SUMMARY OF THE INVENTION

In view of the foregoing background, it is therefore an object of thepresent invention to provide a system and related methods allowing lessexpensive and repeatable interconnection between optical waveguides.

This and other objects, features, and advantages are provided by arepeatable optical waveguide interconnection which may include first andsecond optical waveguides having respective first and second end faces.Each of the first and second optical waveguides may include a corehaving a core index of refraction, and a cladding surrounding the coreand having a cladding index of refraction different than the core indexof refraction. The interconnection may further include a first indexmatching elastomeric solid layer having a proximal face coupled to thefirst end face, and a distal face opposite the proximal face to berepeatably optically coupled to the second end face. The first indexmatching elastomeric solid layer may have an index of refraction profilematching an index of refraction of the core and the cladding. Therepeatable optical waveguide interconnection thus provides a relativelydurable and low-cost approach for repeatably coupling optical waveguidestogether.

More particularly, the proximal end face may be chemically bound to thefirst end face, and the distal end face is low-tack. The low-tack distalface of the first index matching elastomeric solid layer may havesurface properties defining a wetted interface devoid of air pocketswith the second end face when pressed thereagainst. Moreover, theinterconnection may further include a second index matching elastomericsolid layer having a proximal end face chemically bound to the secondend face, and a low-tack distal face opposite the proximal face to berepeatably optically and mechanically coupled to the low-tack distalface of the first index matching elastomeric solid layer.

By way of example, the first index matching elastomeric solid layer maycomprise an acrylate polymer. The first end face may have a canted anglefrom perpendicular to an axis of the first optical waveguide, and thefirst index matching elastomeric solid layer may have a uniformthickness and match the canted angle. Also, the first index matchingelastomeric solid layer may have a central region having a first indexof refraction matching the core at a desired operating wavelength, and aregion surrounding the core having a second index of refraction matchingthe cladding at the desired operating wavelength.

In particular, the first index matching elastomeric solid layer may alsohave a central region having a first graded index of refraction matchingthe core at a desired operating wavelength, and a region surrounding thecore having a second index of refraction matching the cladding at thedesired operating wavelength. In some embodiments, the core of the firstoptical waveguide may be larger than the core of the second opticalwaveguide. By way of example, each of the first and second opticalwaveguides may comprise a multimode optical waveguide. Furthermore, theinterconnection may further include a first ferrule mounting the firstoptical waveguide, and a second ferrule mounting the second opticalwaveguide.

A related method of making a repeatable optical waveguideinterconnection between first and second optical waveguides, such asthose described briefly above, is also provided. The method may includeforming a first index matching elastomeric solid layer having a proximalface coupled to the first end face, and a distal face opposite theproximal face to be repeatably optically coupled to the second end face.The first index matching elastomeric solid layer may have an index ofrefraction profile matching an index of refraction of the core and thecladding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional diagrams of a repeatableoptical fiber interconnection (shown in coupled and uncoupled positions,respectively) including an index matching elastomeric solid layerproviding core index of refraction matching in accordance with theinvention.

FIGS. 2A and 2B are schematic cross-sectional diagrams of an alternativeembodiment of the repeatable optical fiber interconnection of FIGS. 1Aand 1B including first and second index matching elastomeric solidlayers.

FIGS. 3 and 4 are schematic cross-sectional diagrams of an optical fiberhaving an angled end, shown with and without a corresponding indexmatching elastomeric solid layer, respectively, for use in analternative embodiment of the interconnection of FIGS. 1A and 1B.

FIGS. 5A and 5B are schematic cross-sectional diagrams of an alternativeembodiment of the repeatable optical fiber interconnection of FIGS. 1Aand 1B including ferrule mounts for the optical fibers.

FIG. 6 is a flow diagram illustrating method aspects for making theinterconnection of FIGS. 1A and 1B.

FIGS. 7A and 7B are schematic cross-sectional diagrams of a repeatableoptical fiber interconnection (shown in coupled and uncoupled positions,respectively) including an index matching elastomeric solid layerproviding core and cladding index of refraction matching in accordancewith the invention.

FIG. 8 is an end view of the index matching elastomeric solid layer ofFIGS. 7A and 7B.

FIG. 9 is an end view of an alternative embodiment of the index matchingelastomeric solid layer of FIG. 8 having a graded index of refraction.

FIG. 10 is a flow diagram illustrating method aspects for making theinterconnection of FIGS. 7A and 7B.

FIG. 11 is a series of schematic diagrams illustrating a method formaking the index matching elastomeric solid layer of FIG. 8.

FIG. 12 is a schematic cross-sectional diagram of an optical fiberhaving and angled end and a corresponding index matching elastomericsolid layer for use in an alternative embodiment of the interconnectionof FIGS. 7A and 7B.

FIG. 13 is a schematic cross-sectional diagram of an optical fiber andcorresponding ferrule mount for use in an alternative embodiment of theinterconnection of FIGS. 7A and 7B.

FIG. 14 is a schematic cross-sectional diagram of an alternativeembodiment of the interconnection of FIGS. 7A and 7B in which the firstand second optical fibers have different core sizes, and the indexmatching elastomeric solid layer has a graded core portion to therebyprovide a GRIN lens interconnection structure.

FIGS. 15A and 15B are schematic cross-sectional diagrams of an opticalfiber switch (shown in coupled and uncoupled positions, respectively)including an index matching elastomeric solid layer in accordance withthe invention.

FIG. 16 is a flow diagram illustrating a method for making the opticalfiber switch of FIGS. 15A and 15B.

FIG. 17 is a flow diagram illustrating a method for making analternative embodiment of the optical fiber switch of FIGS. 15A and 15Bincluding an index matching elastomeric solid layer providing core andcladding index of refraction matching.

FIG. 18 is a series of tables which may be used to calculate a startingcomposition for an index matching elastomeric solid layer for use ininterconnections and optical fiber switches in accordance with theinvention.

FIG. 19 is a series chemical formulas for exemplary acrylate monomersthat may be used for forming an index matching elastomeric solid layerfor use in interconnections and optical fiber switches in accordancewith the invention.

FIGS. 20 and 21 are chemical formulas for exemplary photoinitiators thatmay be included in the index matching elastomeric solid materialformulation for use in interconnections and optical fiber switches inaccordance with the invention.

FIG. 22 is a graph of measured dispersion of refractive index for indexmatching elastomeric solid core and cladding materials for use ininterconnections and optical fiber switches in accordance with theinvention.

FIG. 23 is a schematic diagram of a fixture for creating angled opticalfibers for use in the optical fiber switch of FIGS. 15A and 15B.

FIG. 24 is a graph of measured to expected fiber-to-fiber loss for anexemplary index matching elastomeric solid material formulation for usein interconnections and optical fiber switches in accordance with theinvention.

FIGS. 25-28 are flow diagrams illustrating additional method aspects formaking optical fiber devices and index matching elastomeric solid layerstherefor in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout, and prime notation is used toindicate similar elements in alternate embodiments.

Referring initially to FIGS. 1A and 1B, a repeatable optical fiberinterconnection 30 illustratively includes first and second opticalfibers 31, 32 having respective first and second end faces 33, 34. Eachof the first and second optical fibers 31, 32 illustratively includes arespective core 35, 36 (e.g., doped silica glass cores) having a coreindex of refraction n₁, and a respective cladding 37, 38 (e.g., plastic)surrounding the core and having a cladding index of refraction n₂ lessthan the core index of refraction. The repeatable optical fiberinterconnection 30 further illustratively includes a first indexmatching elastomeric solid layer 40 having a proximal face 41 chemicallybound to the first end face 33, as represented by the dots in theillustrated embodiment. The chemical bonding may be obtained by properselection of the index matching material and/or various types of surfacetreatments to the end face 33, such as for example with silanecompounds, as would be appreciated by those skilled in the art.Moreover, the first index matching elastomeric solid layer 40 alsoillustratively includes a low-tack distal face 42 opposite the proximalface 41 which may advantageously be repeatably optically coupled to thesecond end face 34 of the second optical fiber 32 as shown. The low-tackdistal face can be obtained by proper selection of the index matchingmaterial (considering its post-cured properties) and/or the addition ofa surface coating, as would also be appreciated by those skilled in theart. As used herein, a “low-tack” surface is one that allows the matedfirst and second optical fibers to be de-mated without causing permanentdeformation of the surface of the index matching material and withoutthe need for excessive force per unit area. By way of example, suchforce may be less than 10 g/mm² and, more particularly, less than 1g/mm², when the material of the second mated object is fused silica.

The first index matching elastomeric solid layer 40 also advantageouslyhas an index of refraction n₁ matching at least the index of refractionn₁ of the cores 35, 36. That is, the index of refraction of the firstindex matching elastomeric solid layer 40 is chosen to be substantiallythe same as that of the cores 35, 36 to be coupled together. This firstindex matching elastomeric solid layer 40 advantageously provides theoptical function of an index matching liquid or gel, but without theabove-noted disadvantages of such materials (e.g., less susceptible tocontamination, etc). Further, by chemically bonding the first indexmatching elastomeric solid layer 40 to the first end face 41, the layermay thereby remain permanently in place while temporary connections arerepeatedly made with the second mating end face 34.

As a result of its index matching, elastomeric solid properties, andchemical bonding to the first end face 33, the layer 40 advantageouslyprovides reduced transmission loss and back reflection. Moreover, italso remains in place indefinitely, and does not migrate as do indexmatching gels and liquids. Additionally, the layer 40 may be moreresistant to dirt and contaminants and may be cleaned, it retains anoptically smooth surface, may be cast or formed into desired shapes, andit may be tailored to a wide range of refractive index values andelastic properties (e.g., modulus, flexibility, etc.), as will beappreciated by those skilled in the art. By way of example, the firstindex matching elastomeric solid layer 40 may comprise an acrylatepolymer. Because acrylates may be patterned using lithography, forexample, they provide the ability to form precise layer structuresshaped and positioned with a relatively high degree of accuracy. Furtherdetails regarding exemplary elastomeric formulations that may be usedfor the layer 40 will be discussed further below.

In some embodiments, the low-tack distal end face 42 may be repeatablydirectly mechanically coupled to the second end face. For example, thelow-tack distal face of the first index matching elastomeric solid layermay have surface properties defining a wetted interface devoid of airpockets with the second end face when pressed thereagainst, therebyproviding in part a mechanical suction coupling with the second matingend face 34 of the second optical fiber 32, as will be appreciated bythose skilled in the art.

In the illustrated embodiments, the optical fibers 31, 32 are multimodefibers. That is, the optical fibers 31, 32 may advantageously supportmany propagation paths or transverse modes, as opposed to single modefibers which support a single mode or propagation path. Multimode fibersgenerally have a larger core diameter, and are used for short-distancecommunication links and for applications where high power transmissionis required, such as in localized networks or between buildings. Assuch, since the addition or replacement of optical fibers may be moreprevalent in localized areas where multimode fibers are used, theability to repeatably optically (and, optionally, mechanically) couplemultimode fibers may be a significant advantage. However, it will beappreciated by the skilled artisan that index matching elastomeric solidlayers as described herein may also be used with single mode opticalfibers, which are typically employed for relatively long communicationlinks.

Referring now additionally to FIG. 2, an alternative embodiment of arepeatable optical fiber interconnection 30′ illustratively includes asecond index matching elastomeric solid layer 43′. The second layer 43′is similar to the first layer 40′, in that it has a proximal end face44′ chemically bound to the second end face 34′ of the second opticalfiber 32′, and a low-tack distal face 45′ opposite the proximal end faceto be repeatably optically and mechanically coupled to the low-tackdistal face 42′ of the first index matching elastomeric solid layer 40′.

As shown in FIG. 3, in some embodiments the first end face 34″ may havea canted angle from perpendicular to an axis 46″ of the first opticalfiber 31″. In such embodiments, the first index matching elastomericsolid layer 40″ may have a uniform thickness and match the canted angle,as shown in FIG. 4. As such, the interconnection may advantageously beused in applications where not only perpendicular optical fiber endfaces are used, but also in applications where angled optical fiber endsfaces require repeatable optical coupling, such as in optical switches,which will be discussed further below.

The layer 40″ is tailored to form an extension of the optical fiber 31″,and to conform to the angle of the end face of the fiber. A high degreeof light transmission may advantageously be maintained between the twooptical fibers 31″, 32″ as a result of the layer 40″, whereas withoutthis layer little or no light would be transmitted therebetween.Moreover, the elastomeric nature of the layer 40″ advantageously allowssmall discontinuities in the mating faces to be uniformly filled, thusreducing the loss of light through reflection and scattering at theinterface, as will be appreciated by those skilled in the art.

Yet another embodiment of the repeatable optical fiber interconnection30′″ is now described with reference to FIGS. 5A and 5B. In theillustrated example, a first ferrule mounting 50′″ for the first opticalfiber is provided, along with a second ferrule mounting 51′″ for thesecond optical fiber. As will be appreciated by those skilled in theart, in fiber optic terminations, precision ferrules are sometimesdesirable to assist with connecting two fibers together. The first andsecond fibers 31′″ and 32′″ are shown optically coupled together in FIG.5B.

A related method of making a repeatable optical fiber interconnectionbetween the first and second optical fibers 31, 32 is now described withreference to FIG. 6. Beginning at Block 60, the method illustrativelyincludes forming a first index matching elastomeric solid layer 40having a proximal face 41 chemically bound to the first end face 33 ofthe first optical fiber 31, and a low-tack distal face 42 opposite theproximal face, at Block 61. As noted above, the low-tack distal face 42is to be repeatably optically coupled to the second end face 34 of thesecond optical fiber 32, thus concluding the illustrated method (Block62).

Turning now to FIGS. 7A, 7B, and 8, another embodiment of a repeatableoptical fiber connection 130 illustratively includes an index matchingelastomeric solid layer 140 having an index of refraction profilematching an index of refraction of the core 135 and the cladding 137.More particularly, the layer 140 illustratively includes a first portion148 having an index of refraction n₁ matching the index of refraction ofthe core 135, and a second portion 149 having an index of refraction n₂matching the index of refraction of the cladding 149. As with theabove-described structure, the layer 140 is chemically bonded to theoptical fiber 131. The layer 140 thereby provides a light guidingstructure, i.e., an optical waveguide. That is, the layer 140 mayadvantageously be tailored to form an extension of the optical fiber131, providing for the preservation of the propagating optical mode(s).Furthermore, the elastomeric nature of the layer 140 allows smalldiscontinuities in the mating faces 131, 132 to be uniformly filled,thereby preventing the loss of light through reflection and scatteringat the interface. The mode matched guiding structure thus advantageouslyprovides for reduced loss and back reflection.

As also noted above, acrylates and copolymers with urethanes andthiolenes are advantageous materials for forming the layer 140, as theymay provide desired optical matching and may be precisely patternedusing techniques, such as lithography or molding, with a relatively highdegree of accuracy. Moreover, these materials may advantageously be usedto create different index profiles for the first portion 148. Moreparticularly, an alternative embodiment of the layer 140′ is shown inFIG. 9, in which the first portion 148′ has a graded index ofrefraction, as opposed to the first portion 148 of FIG. 8 which hasradially uniform index of refraction matching the core 135′ at a desiredoperating wavelength, as will be appreciated by those skilled in theart. The graded portion 148′ may be particularly useful in GRIN lensapplications, as will be discussed further below.

Another method of making a repeatable optical fiber interconnectionbetween the first and second optical fibers 131, 132 is now describedwith reference to FIG. 10. Beginning at Block 60′, the methodillustratively includes forming a first index matching elastomeric solidlayer 140 having a proximal face 141 chemically bound to the first endface 133 of the first optical fiber 131, and a low-tack distal face 142opposite the proximal face, at Block 61′. As noted above, the low-tackdistal face 142 is to be repeatably optically coupled to the second endface 134 of the second optical fiber 132, thus concluding theillustrated method (Block 62′).

An exemplary approach for forming the layer 140 with the first andsecond portions 148, 149 will now be discussed with reference to FIG.11. Forming the first portion 148 of the layer 140 initially involves apatterned exposure of the core material, which may advantageously beaccomplished with a proximity exposure through a glass mask, afterspinning the core formulation on a substrate 109, such as a siliconsubstrate, for example, at step 110. In some embodiments, the coreformulation may be formed directly on the end of the optical fiber 131rather than the substrate 109. A contact exposure may be employed inwhich the liquid monomer fills the region between the mask and thesubstrate 109. The first portion 140 may then be patterned anddeveloped, at step 111, followed by injection of a cladding formula atstep 112. The cladding may be restricted to form only on the sides ofthe core by using a cover plate 113 as illustrated, and allowing osmoticforces to fill the space between substrate and the glass cover plate 113with cladding monomer.

If a graded index is desired, the core or first portion 148 may bepartially cured to a level sufficient to define the core, and the liquidcladding formulation may be allowed to exchange monomers with the coreby allowing the assembly to soak at some elevated temperature (e.g., 40to 60° C., although other temperatures may be used in differentembodiments), at step 114. The degree of grading will depend on time,temperature, and the percentage of cure in the patterned core, as willbe appreciated by those skilled in the art. In general, for a gradedindex guide it is desirable that the monomers in each formulationinclude two or more monomers that have relatively widely spacedrefractive indexes and differing rates of cure, allowing monomers thathave different refractive indexes to be readily diffused into and/or outof the core region, as will also be appreciated by those skilled in theart.

If a thermal soak is not being used to provide a graded index, theinjected clad formulation may simply be allowed to stand at roomtemperature for a sufficient amount of time to allow the claddingportion 149 to spread around the core portion 148. A second UV exposuremay be performed at step 115, after which the layer 140 may remainbonded on the substrate for packaging or handling, at step 116, orremoved from the substrate 116 to provide a free standing layer to becoupled to the optical fiber 131, at step 117. In accordance with oneexemplary implementation, the layer 140 may be peeled from the substrate109 while still attached to the glass cover plate 113. A mask size of62.5 microns in diameter was used in one exemplary implementation, andthis diameter was essentially reproduced in the size of the core.Deviations in the diameter may advantageously be produced by under orover exposure or by under development, if desired, as will beappreciated by those skilled in the art.

Additional configurations that may be produced using variations of theabove-described approach are illustrated in FIGS. 12-14. An opticalfiber 131′ with a canted end face, and corresponding index matchingelastomeric solid layer 140′ with a uniform thickness and matching thecanted angle of canted end face, is shown in FIG. 12. Similar to theembodiment illustrated in FIGS. 5A and 5B, another exemplary embodimentwith a ferrule mounting 150′ and an index matching elastomeric solidlayer 140″ with first (core matching) and second (cladding matching)portions 148″, 149″ may also be provided, as seen in FIG. 13. In theembodiment illustrated in FIG. 14, the index matching elastomeric solidlayer 140′ includes a first (core) portion 148′″ with a graded index ofrefraction, in which the layer is positioned between first and secondoptical fibers 131′″, 132′″ to thereby provide an integral GRIN lensmounted on a ferrule 150′″, as will be appreciated by those skilled inthe art.

Referring now to FIGS. 15A and 15B, an exemplary optical fiber switch230 including an index matching elastomeric solid layer 240illustratively includes first and second angled optical fibers 201, 202,which may be multimode or single mode fibers. More particularly, theswitch 230 is shown in a coupled or closed position (switch state 1) inFIG. 15A, and an uncoupled or open position (switch state 2) in FIG.15B. In the coupled position, light is transmitted along the path A-A′(i.e., between the two cores 235 and 237), and in the uncoupled positionalong the path A-B (i.e., within the first optical fiber 231) and/or thepath B′-A′ (i.e., within the second optical fiber 232).

Each of the first and second angled optical fibers 201, 202,illustratively includes respective first and second end faces 203, 204.As with the above-described embodiments, an index matching elastomericsolid layer 240 is included and has a proximal face coupled to the firstend face 203, and a distal face opposite the proximal face to berepeatably optically coupled to the second end face 204. Here again, theindex matching elastomeric solid layer 240 has an index of refractionmatching the index of refraction of the core, as shown in FIGS. 1A and1B. The optical fiber switch 200 may also include one or more actuators255 (e.g., a piezoelectric actuator(s)) for relatively moving the firstand second angled optical fibers 231, 232 between the coupled anduncoupled positions, as will be appreciated by those skilled in the art.

A related method for making the optical fiber switch 230 is illustratedin FIG. 16. Beginning at Block 160, the first and second angled opticalfibers 231, 232 are formed, each having respective first and second endfaces (Block 161). As noted above, each of the first and second angledoptical fibers 231, 232 illustratively includes a core 235, 237 having acore index of refraction n₁, and a cladding 236, 238 surrounding thecore and having a cladding index of refraction n₂ different than thecore index of refraction. The method further illustratively includesforming an index matching elastomeric solid layer 140 having a proximalface coupled to the first end face 203, and a distal face opposite theproximal face to be repeatably optically coupled to the second end face204, at Block 162. Here again, the index matching elastomeric solidlayer 204 has an index of refraction matching at least the index ofrefraction n₁ of the core 235. The method also illustratively includespositioning one or more actuators 255 for relatively moving the firstand second angled optical fibers 231, 232 between the coupled position(FIG. 15A) and the uncoupled position (FIG. 15B), at Block 163, thusconcluding the illustrated method (Block 164).

In some embodiments, the optical switch may include an index matchingelastomeric solid layer matching both the core and the cladding, asdiscussed above with reference to FIGS. 7A and 7B. A related method formaking such an optical switch is illustrated in FIG. 17, in which theindex matching elastomeric solid layer is formed to have an index ofrefraction matching the core and cladding indexes of refraction, atBlock 162′. It should also be noted that in some optical fiber switchembodiments, a second index matching elastomeric solid layer may bechemically bonded to the second face 204 of the second optical fiber232, as similarly discussed above with reference to FIGS. 2A and 2B, aswill be appreciated by those skilled in the art.

Generally speaking, desirable characteristics of a multimode switchinclude achieving stringent requirements of low insertion loss, lowreturn loss, and fast switching time. However, such characteristics aregenerally difficult to achieve in a multimode switch. Typically,multimode switches are of a mechanical type utilizing moving fibers ormoving optical elements (e.g. mirrors). Achieving the fast switchingtime requires micro-electromechanical systems (MEMS) scale components toreduce the moving mass. Designs that reduce the extent of the requiredmotion also are desirable. Moreover, precise alignment of the switch inthe coupled switch state, angling of the waveguide faces, and/or carefulindex matching within the interface between guides are also typicallydesirable. Reduction of any unguided light paths is also a significantconsideration.

These characteristics may advantageously be achieved with the switch200, which operates on the principle of frustrated total internalreflection (FTIR). The switch 200 requires only a short degree of motionbetween the first and second end faces 203, 204. Generally, the requireddisplacement need be only about 3 wavelengths (e.g., 4 microns) or lessto operate the switch 200. The switch may be designed with a 45-degreeor greater angle (α) interface, so that back reflection in state 1(coupled position) will be strongly suppressed. As noted above, theswitch 200 may accomplish either of two switch states, namely (1) A toA′ (i.e., coupled) and (2) A to B and/or B′ to A′ (uncoupled). Theswitch 200 may be built as a half 2×2 crossbar switch, or it may beassembled from two 1×2 switches, as will be appreciated by those skilledin the art.

Exemplary optical fiber switch implementations will now be describedwith reference to FIGS. 18-24. In the following examples, the indexmatching elastomeric solid layer is referred to as an elastomeric indexmatching medium (EIMM). In the case where EIMM is constructed as a lightguide, it may have a core oriented at a 45-degree or greater angle tothe plane of the film, and sized to match the core of the fiber (e.g.,50 or 62.5 μm). As shown in FIGS. 15A and 15B, the core is aligned withthe fiber to which the EIMM is mounted.

In those embodiments where the core region 148 of the EIMM may also begraded in index, light is advantageously allowed to propagate throughthe EIMM just as it does through the fiber itself. This provides forreduced loss, and allows the EIMM to be of different thicknesses asneeded to satisfy the mechanical aspects of the given design. In state 2(i.e., uncoupled), a significant portion of the light will be reflectedat the interface between the EIMM and air. As will be appreciated bythose skilled in the art, variations of the basic design shown in FIGS.15A and 15B are possible. Some potential variations would include theuse of stationary mirrors or lenses to collect or insert the light inpaths B and B′, for example. Moreover, other types of actuators may alsobe used.

Various EIMM polymer formulations may be used for the repeatable opticalfiber interconnection and optical fiber switches discussed above.Generally speaking, the EIMM polymers may be formed through UV curing ofacrylates and/or methacrylates. Fabrication of the polymer may beginwith a formulation of liquid acrylate and/or methacrylate (abbreviatedherein as (meth)acrylate) monomers with a small amount of aphotoinitiator and an antioxidant. The index of refraction of themonomers at 589.3 nm (sodium D line) is provided by the manufacturer.For optical fiber applications, the index of the polymer at 1310 nmand/or at 850 nm is of particular interest. Polymers made with differentmonomer formulations will have both a different index and a differentdispersion, as will be appreciated by those of skill in the art.

An initial estimate may be used to determine the refractive index as afunction of the relative amounts of the monomers in the startingformulation. This estimated formulation may be used as a starting point,and then small additions of specific monomers may be used based uponactual measurements to refine the targeted refractive index formulationfor the desired polymer. FIG. 18 provides an exemplary set of tableswhich may be used to calculate the starting composition of a liquidmonomer formulation. Since the photoinitiator and the antioxidantrepresent a small fraction of the total volume, they are ignored in thecalculation.

Table 18.1 provides input values describing the characteristics of theliquid monomers and the volume percentages of each monomer that aretargeted for use. The empirical parameters in the first two columns ofTable 18.3 give a measure of expected change to be incurred as a resultof polymerization (δ), and the expected shift in the index in going from589 nm to 1310 or 850 nm as a result of dispersion (ξ) δ is estimated bythe ratio of index at 589.3 nm between the liquid monomer and the curedpolymer. The dispersion factor, ξ, is the ratio of the index of thepolymer at the target wavelength (850 or 1310 nm) and the index at 589.3nm. These parameters are obtained from measurements on closely relatedacrylate polymers. The calculated values are highlighted in the lastthree columns of Table 18.3. In the illustrated example, the NA ofCorning InfiniCor SX 50-μm fiber is 0.200, so the volume percentages ofthe various monomers are adjusted to reach this value. The calculationof the expected refractive index is made with Eq. (1) below, whereVf_(i) represents the volume fraction of the i^(th) component, δ is thepolymerization factor, and ξ is the dispersion factor at 1310 or 850 nm:n _(polymer)=(n _(A) *Vf _(A) +n _(B) *Vf _(B) +n _(C) *Vf _(C) +n _(D)*Vf _(D) +n _(E) *Vf _(E))*δ*ξ.  (1)

Exemplary switches were designed around two graded-index fiber types:InfiniCor SX (50 μm) and Corning InfiniCor CL-1000 (62.5 μm) fromCorning, Inc., of Corning, N.Y. Systems operating at 850 nm would tendto use InfiniCor SX, while those operating around 1310 nm would tend touse InfiniCor CL-1000, although either fiber type may be used withineither wavelength region. Since the EIMM is designed to provide indexmatching, it is significant to characterize the index of refraction ofthe respective fibers at the wavelengths of interest, and a summarythereof is provided in the following table of measured and specifiedparameters for Infinicor fibers.

Peak NA Wavelength Core Clad Δ from Peak from Fiber Type (nm) IndexIndex Δn Δ Spec NA Spec InfiniCor SX 850 1.46735 1.4525 0.01485 1.01%1.00% 0.208 0.200 InfiniCor CL 1000 1322 1.4753 1.4467 0.0286 1.92%2.00% 0.289 0.275

As discussed above, the elastomeric index matching medium may be a(meth)acrylate polymer that is synthesized from acrylate andmethacrylate monomers by UV curing. Monomers are selected on the basisof a variety of criteria covering the desired properties of the polymer,such as refractive index, hardness, modulus, toughness, and clarity, aswill be appreciated by those skilled in the art. Monomers having lowerhealth risks or toxicity may also be favored. Polymers of low tomoderate hardness are also generally desirable, so that effectivewetting of the optical contact surface may be readily achieved when theswitch is in the closed or coupled (A-to-A′) position. The modulus willdetermine the force necessary to achieve a wetted spot covering theentire core (and optionally cladding) region of the fiber.

One exemplary selection of acrylate monomers is shown in FIG. 19. Eachmonomer contributes unique attributes. The fluorinated compounds, F8DAand TFPM, are used to lower refractive index of the formulation to matchthe refractive index of the fiber core and cladding. The aromaticcompound, EBDA-10, contributes a higher index to the core via thepresence of phenyl groups. By virtue of its long pendant chains ofethoxy groups, it also imparts flexibility, toughness and reduceshardness. The aliphatic diacrylate, PNGDA, also has intermediaterefractive index with desired mechanical flexibility, and in combinationwith F8DA or EBDA-10, allows the index of the cladding and/or the coreto be adjusted up or down. The monofunctional monomers, TFPM, IBA andIOA, allow the crosslink density to be adjusted, which influenceshardness and toughness. These monomers may also be used to adjust theglass transition temperature (Tg) of the polymer up or down, since thehomopolymer of IBA has a relatively high Tg (90° C.) and that of IOA hasa relatively low Tg (−54° C.). Generally speaking, a combination ofthese or other suitable monomers may be used which are miscible and notsubject to phase separation upon polymerization. The following tableprovides a listing of the physical characteristics of several exemplarymonomers:

Est. Liq. Tg of RI of Liq. Surface Loss Viscosity Density Homopolymer @589 Tension @1310 Material MW (cp) (kg/L) (° C.) nm (dyn/cm) dB/cmEBDA-10 776 610 1.126 2 1.5142 37.6 0.20 EBDM-30 2156 610 1.122 −431.4906 43.8 0.17 PNGDA 328 15 1.005 32 1.4500 32.0 0.20 IDA 184 5 0.88−54 1.4346 28.0 0.22 F8DA 370 0.46 1.383 1.3937 24.2 0.09 TFPM 200 1.21568 1.3730 20.6 0.11

The above-noted monomers include both monofunctional and difunctionalmonomers, that is, they contain either one or two (meth)acrylate groups.These groups are subject to a free-radical polymerization mechanism thatleads to a heavily crosslinked solid that has elastomeric properties. Toinitiate polymerization with UV light, a UV-sensitive photoinitiator isincluded in the formulation. Also, to reduce the tendency to yellow withage, an antioxidant is added. Each of these components is present onlyas a small percentage of the formulation, e.g., at a 2% or lower level.As already noted, one desirable aspect of the formulation is thatconstituent components are miscible, and remain so as polymerizationoccurs. Phase separation may lead to haze formation, and thus opticalscattering loss. Exemplary formulations are listed in the table below:

Elastomeric Index Matching Material Formulations EIMM 200 EIMM 200 EIMM401 EIMM 401 Core Clad Core Clad Formulation Formulation FormulationFormulation Abbreviation (weight %) (weight %) (weight %) (weight %)Materials Isooctyl acrylate IOA 28.3% Perfluorohexanediol F8DA 79.0%26.4% 26.6% 35.1% diacrylate Propoxylated neopentyl PNGDA 21.0% 26.0%21.3% 15.6% glycol diacrylate Tetrafluoropropyl TFPM 19.3% 25.6% 32.8%methacrylate Ethoxylated (10) EBDA-10 26.6% 16.6% bisphenol A diacrylateAdditives⁽¹⁾ Diethoxyacetophenone DEAP 2.0% 2.0% (Photoinitiator)Daracur 4265 D-4265 2.0% 2.0% (Photoinitiator) Irganox 1010 I-1010 0.3%0.3% 0.3% 0.3% (Antioxidant) Additives taken as a percent of the totalof the materials list

By way of example, Irganox 1010 from Ciba of Basel, Switzerland may beused as a suitable antioxidant. Moreover, two suitable liquidphotoinitiators are shown in FIGS. 20 and 21. Both of the illustratedphotoinitiators have a desirable response to UV light from a mercurylamp (I-line). The D4265 has the strongest response, but also includessome sensitivity to blue light as well (H-line), so it may requirestorage and use in an area with filtered (yellow-light) illumination, aswill be appreciated by those skilled in the art.

Several material formulations made with the above monomers andphotoinitiators were characterized in terms of their index of refractionand dispersion characteristics. Samples of core and cladding were coatedon a silicon substrate and exposed to a dose of 1500 mJ of UV light froma high-pressure mercury light source that outputs approximately 35mW/cm². The cured samples were then annealed under flowing nitrogen for1 hour at 125° C. The annealing procedure has the potential to sublimeaway any low molecular weight species, such as residual uncured monomerand the photoinitiators. The refractive index was measured by a prismcoupling measurement on thin films (typically 10 to 50 microns inthickness). Results for the formulation designated EIMM-200 from FIG. 18are shown in FIG. 7. These results are for the formulations of EIMM-200core and cladding, which are in line with the values for the InfiniCorSX fiber listed above (and plotted as black squares in the graph of FIG.18).

As noted above, it may be desirable to design the mechanical propertiesof the EIMM to match the characteristics needed for the given switch.For example, measurements may be made on the materials formulated usinga Differential Scanning Calorimeter (DSC) to determine glass transitiontemperature (Tg), and a Dynamic Mechanical Analyzer (DMA) to determinestorage modulus. These values, along with refractive indexes, arerecorded in the following table. The data demonstrates that themechanical and thermal properties may be varied over a very large rangethrough the choice of different recipes for the monomer formulations.

Measured Characteristics of Acrylate Polymer Films⁽¹⁾ Modulus⁽³⁾ @ Est.Solid Rl @ Rl @ Tg⁽²⁾ 30° C. Density Formulation 1322 nm 850 nm (° C.)(kpsi) (g/cm3) 1a Core 1.4895 7.44 0.3 1.08 1b Core 1.4904 11.6 14.51.08 1a Clad 1.4703 37.3 143.8 1.04 1b Clad 1.4685 32.7 137.5 1.08 2Core 1.4669 9.3 to 60⁽⁴⁾ 2 Clad 1.4525 2 ⁽¹⁾Solid polymer after annealat 125 C. for 1 hr under nitrogen. ⁽²⁾Tg determined from 1st heating inDifferential Scanning Calorimeter (DSC) ⁽³⁾Modulus from DynamicMechanical Analysis (DMA) ⁽⁴⁾Range depending on cure and thermal history

Monomer Formulations for Selected Elastomeric Solids F8DA PNGDA EBDA-10TFPM IOA DEAP D-4265 I-1010 Formulation (wt %) (wt %) (wt %) (wt %) (wt%) (wt %) (wt %) (wt %) 1a Core 59.4 38.3 2 0.3 1b Core 59.4 38.3 2 0.31a Clad 2.8 94.9 2 0.3 1b Clad 10.7 82.3 4.7 2 0.3 2 Core 77.2 20.5 1 10.3

The EIMM structure or layer may take various forms, one of which is alayer of material that has an index equaling the effective index of thefiber. Again, the EIMM is advantageous over liquid index matchingmaterials in applications such as those shown in FIGS. 15A and 15Bbecause obtaining total internal reflection from the facetted (angled)fiber ends requires an air interface. A liquid would need to be cleanlyremoved upon cycling of the switch. The solid EIMM accomplishes thisrequirement on one or both faces, and can optionally form a planarreflective surface in switch state 2 (uncoupled), if left on one of thefiber end facets. The EIMM may be prepared as a free-standing film andsubsequently aligned and applied to the fiber end face, or it may befabricated directly on the fiber end or polished ferrule, as discussedabove with reference to FIG. 11. In the former case it is grown on glassor silicon and peeled off after curing. In the latter case, an adhesionpromoter may be applied to the fiber end, and the EIMM would then remainrigidly attached, as will be appreciated by those skilled in the art.

To fabricate the waveguide on the end of a fiber, the 50-micron corefiber may be angled at 51 degrees to provide total internal reflectionat the fiber end for the supported light rays. The waveguide may becoaxial with the fiber. One exemplary fixture 300 for creating thisgeometry is shown in FIG. 23. The optical fiber 331 may be mounted in asilicon V-groove block 301 and polished at a 51-degree angle, forexample. The fiber 331 may remain in the block 301 during the EIMM layer340 fabrication step. Wire spacers 302 may be used to establish athickness (t) for the EIMM layer 340, and a mask 303 may be used todefine an oval core portion 348 matching the core 335 of the fiber 331,as shown in FIG. 24. Once the mask 303 is properly aligned with the core335 of the fiber 331, the fixture 300 will be oriented at a 51-degreeangle as shown for UV exposure from a vertically collimated lightsource. A coupling prism 304 may be attached to the mask 303 to allowthe UV beam to propagate at a 51-degree angle through the mask and theliquid EIMM monomer, as will be appreciated by those skilled in the art.The mask 303 and the prism 304 may both be made from quartz (silica) andhave a refractive index similar to or the same as the EIMM. As the EIMMcures its index will increase, hence there will be some refraction ofthe UV beam as indicated between the solid and dashed lines for the pathof the UV beam.

After the core exposure, the structure may be developed using a solventmixture of methanol and isopropanol, for example. A second mask (notshown in FIG. 23) including the cladding structures may be used todefine a cladding portion 349 that follows the cladding 337 of the fiber331, as discussed above with reference to FIG. 11. Again, this willproduce an EIMM layer 340 on the end of the fiber 331 that has the samegeometry as the fiber itself, ending in a 51-degree angle, which willreflect light transversely when the endface is in air and transmit lightcoaxially when a mating fiber is in contact with the EIMM layer 340.

Exemplary thicknesses which may be used for the EIMM layer 340 inoptical fiber switching and interconnection applications may be in arange from about 25 μm to 75 μm, for example, although other thicknessesmay also be used. For such thicknesses, a 1-μm deformation of the layer340 upon closure of the switch will result in a strain that lies betweenabout 4% and 1.3%, respectively. It should be noted that the effectivehardness of the layer 340 will be related to the thickness, since forsuch thin films the hardness of the substrate influences the effectivehardness of the polymer.

The EIMM layer 340 may advantageously conform to irregularities at theinterface of two temporarily conjoined optical fibers to reducereflections or scattering losses. A test for pairs of fibers polished ata 45-degree angle was performed which validated this function. For thetest, the EIMM polymer was grown on the surface of a fiber polishingblock in the shape of a 1 mm×1 mm pad that covered the fiber end. Asecond fiber also held in its polishing block, but not covered by EIMM,was then used to make an optical connection to the first fiber. Thisconnection was achieved through active alignment, and the minimumtransmission loss and maximum reflection loss as measured with anoptical time-domain reflectometer (OTDR) were recorded. The testemployed Corning InfiniCor CL 1000 62.5-μm fiber. For the test there wasno guide structure in the EIMM layer, just a continuous coating of anEIMM material that matched the peak index of the graded index fiber, aswill be appreciated by those skilled in the art.

Data taken with various thicknesses of the EIMM are presented in thefollowing table:

Measured and calculated loss for 1310-nm light transmission through agap filled with EIMM Calculated Loss Separation for 62.5 Fiber Data * @1310 RL (μm) (dB) (dB) (dB) 5 0.034 10 0.068 25 0.173 0.175 59 50 0.3530.306 71 100 0.738 1.037 75 * Using pad of EIMM-12 Core of thickness (s)As may be seen, desirable return losses may be achieved (e.g., greaterthan 70 dB). For the thinnest sample, it is theorized without wishing tobe bound thereto that the blocks may not have been sufficiently parallelto allow full approach and optimization of the RL. It should also benoted that the transmission losses were also essentially as low astheory will allow, given that there was no guiding structure. For agraded index fiber of a given NA and radius, a, the expectedfiber-to-fiber loss for propagation in a gap, s, filled by a material ofindex, n₀, the following equation represents an expected gap lossrelation:

${{Gap\_ Loss}({dB})} = {{{- 10} \cdot \log}\left\{ {1 - \frac{s \cdot {NA}}{4 \cdot a \cdot n_{0}}} \right\}}$

Data from the above relation is presented for comparison in FIG. 24. Itwill be noted that the separations of less than about 15 μm may resultin transmission loss less than 0.1 dB, even if no waveguide structure ispresent in the EIMM. As such, the EIMM layer 340 is an effective indexmatching medium that both suppresses back reflection and enhancestransmission, as will be appreciated by those skilled in the art.

Turning additionally to FIGS. 25 and 26, a method for making an opticaldevice, such as the interconnection 130 discussed above, is nowdescribed. However, it should be noted that the techniques describedbelow may also be applied to other optical fiber devices, such as theoptical fiber switch 230, optical waveguides, etc. Beginning at Block400, a first precursor for a curable index matching elastomeric solidlayer 140 is applied onto an end face 133 of an optical guide device,such as an optical fiber 131, at Block 401. Other optical guide devicesmay include a waveguide that is part of a planar optical circuit, anoptical chip such as a laser, modulator or other optical component, forexample. It should be noted that one or more surface treatmentoperations (e.g., chemical and/or mechanical polishing) may be performedprior to application of the first precursor, at Block 407′. Moreover, anadhesion promoter, such as an alkoxysilane or a Chlorosilane, may beinitially applied to the end face 133 of the fiber 131, if desired.

As discussed above, the first precursor may include one or morepartially fluorinated acrylate monomers, which are helpful for indexmatching of silica. Further, to obtain a desired elastomeric structurethat maintains a desired shape, at least some portion of amultifunctional monomer may also be included. Additionally, to obtain arelatively low modulus, which is desirable to allow filling of gaps andsurface irregularities during, for example, the mating of two fibers,some portion of the precursor may be a monomer that includes relativelyflexible side chains and/or linkages between functional acrylate groups(e.g., generally reflected by having a relatively low glass transitiontemperature for the homopolymer, such as less than 25° C. and, moreparticularly, less than 0° C., for example). Furthermore, it may also bedesirable that the monomers in the precursor be miscible in theproportions necessary to achieve the above-described attributes, and oneor more of the monomers may be liquid at room temperature. Generallyspeaking, the photoinitiator to be included in the precursor may have arelatively high activity and may be soluble to at least 1%, and moreparticularly to about 2%, in the liquid formulation of monomers. Again,suitable examples of such monomers and photoinitiators are discussedabove with reference to FIGS. 19-21.

The method further illustratively includes selectively curing the firstprecursor to form a core portion 148 of the index matching elastomericsolid layer 140 on the end face 133 to have an index of refraction n₁matching the index of refraction of the core 135, at Block 402. Asdiscussed above, this may be done using electromagnetic (EM) radiation,such as UV light, for example (Block 402′). The method may also includeremoving uncured portions of the first precursor, at Block 403, andapplying a second precursor for the curable index matching elastomericsolid layer 140 onto the end face 133 of the optical fiber 131surrounding the core portion 148 of the index matching elastomeric solidlayer, at Block 404. The second precursor may include similar componentsto those discussed above, but adjusted for the different index ofrefraction n₂ of the cladding 137. If a graded index is to be produced,then a set of different monomers that have a difference inpolymerization (or cross linking) rate and/or difference in index ofrefraction may be used (Block 404′), as will be appreciated by thoseskilled in the art. As noted above, an operation such as performing asoak at an elevated temperature may be used to provide the graded indexstructure, at Block 408′.

The method further illustratively includes curing the second precursorto form the cladding portion 149 of the index matching elastomeric solidlayer 140 on the end face 133 to have an index of refraction n₂ matchingthe index of refraction of the cladding, at Block 405, thus concludingthe method illustrated in FIG. 25. Here again, the curing may beachieved through the use of EM radiation, e.g., UV light having theappropriate wavelength to activate the photoinitiator.

In instances where the elastomeric solid layer 140 is to be employed inthe interconnection of dissimilar optical fibers or waveguides, wherethe refractive indices of the respective core and cladding may differbetween the fibers and/or waveguides to be connected, the core andcladding indices may advantageously lie between those of theinterconnected fibers or waveguides. Choosing an intermediate value forthe refractive index of the core of the elastomeric solid layer, as forexample, the average of the refractive indices of the cores of thewaveguides to be interconnected, can provide a reduction in the opticalpower lost in the interconnection. Likewise, choosing an intermediatevalue of the refractive index for the cladding as well as the core ofthe elastomeric solid layer can further reduce losses in theinterconnection. Creating multiple layers of the elastomeric solid wherethe refractive index of the core and the cladding are progressivelychanged in a stepwise manner between the values of the two dissimilarfibers or waveguides can lead to even further decrease in loss, as willbe appreciated by those skilled in the art.

A related method for making an index matching elastomeric solid layer140 to be positioned onto the end face 133 of an optical fiber 131 isnow described with reference to FIG. 27. This method is similar to theone described above with reference to FIGS. 25 and 26, but in thisexemplary embodiment the first precursor is applied onto a substrate109, as described above with reference to FIG. 11 (Block 401″). Aftercuring of the second precursor, the index matching elastomeric solidlayer 140 may be removed from the substrate 109, at Block 410″, forsubsequent placement on an optical fiber, for example, as discussedfurther above.

A similar method for making an optical fiber device, such as theinterconnection 30, is now described with reference to FIG. 28.Beginning at Block 420, the method illustratively includes applying atleast one precursor for a curable index matching elastomeric solid layer40 onto an end face 33 of an optical fiber 31, at Block 421. The atleast one precursor is then cured to form the index matching elastomericsolid layer 40 on the end face 33 to have an index of refraction n₁matching the index of refraction of at least the core 35, at Block 422,thus concluding the illustrated method (Block 423). In some embodiments,the curable index matching elastomeric solid layer 40 may also match theindex of refraction n₂ of the cladding 37, as discussed above.

Additional features of the invention may be found in the co-pendingpatent applications filed concurrently herewith and assigned to theAssignee of the present invention entitled A REPEATABLE OPTICALWAVEGUIDE INTERCONNECTION INCLUDING AN INDEX MATCHING ELASTOMERIC SOLIDLAYER AND RELATED METHODS, Ser. No. 12/610,404; attorney OPTICAL FIBERSWITCH INCLUDING AN INDEX MATCHING ELASTOMERIC SOLID LAYER AND RELATEDMETHODS, Ser. No. 12/610,420; and OPTICAL FIBER SWITCH INCLUDING ANINDEX MATCHING ELASTOMERIC SOLID LAYER PROVIDING CORE AND CLADDING INDEXOF REFRACTION MATCHING AND RELATED METHODS, Ser. No. 12/610,432, andMETHOD FOR MAKING AN OPTICAL FIBER DEVICE INCLUDING A CURABLE INDEXMATCHING ELASTOMERIC SOLID LAYER, Ser. No. 12/610,458, the entiredisclosures of which are hereby incorporated herein in their entirety byreference.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

1. A repeatable optical waveguide interconnection comprising: first andsecond optical waveguides having respective first and second end faces,each of said first and second optical waveguides comprising a corehaving a core index of refraction, and a cladding surrounding said coreand having a cladding index of refraction different than the core indexof refraction; and a first index matching elastomeric solid layer havinga proximal face coupled to the first end face and a distal face oppositethe proximal face to be repeatably optically coupled to the second endface, said first index matching elastomeric solid layer having an indexof refraction profile matching an index of refraction of said core andsaid cladding.
 2. The repeatable optical waveguide interconnection ofclaim 1 wherein said proximal end face is chemically bound to the firstend face; and wherein the distal end face is low-tack.
 3. The repeatableoptical waveguide interconnection of claim 2 wherein the low-tack distalface of said first index matching elastomeric solid layer has surfaceproperties defining a wetted interface devoid of air pockets with saidsecond end face when pressed thereagainst.
 4. The repeatable opticalwaveguide interconnection of claim 2 further comprising a second indexmatching elastomeric solid layer having a proximal end face chemicallybound to the second end face and a low-tack distal face opposite theproximal face.
 5. The repeatable optical waveguide interconnection ofclaim 1 wherein said first index matching elastomeric solid layercomprises an acrylate polymer.
 6. The repeatable optical waveguideinterconnection of claim 1 wherein said first end face has a cantedangle from perpendicular to an axis of said first optical waveguide; andwherein said first index matching elastomeric solid layer has a uniformthickness and matches the canted angle.
 7. The repeatable opticalwaveguide interconnection of claim 1 wherein said first index matchingelastomeric solid layer has a central region having a first index ofrefraction matching the core at a desired operating wavelength, and aregion surrounding the core having a second index of refraction matchingthe cladding at the desired operating wavelength.
 8. The repeatableoptical waveguide interconnection of claim 1 wherein said first indexmatching elastomeric solid layer has a central region having a firstgraded index of refraction matching the core at a desired operatingwavelength, and a region surrounding the core having a second index ofrefraction matching the cladding at the desired operating wavelength. 9.The repeatable optical waveguide interconnection of claim 1 wherein thecore of said first optical fiber is larger than the core of said secondoptical fiber.
 10. The repeatable optical waveguide interconnection ofclaim 1 wherein each of said first and second optical fibers comprises amultimode optical fiber.
 11. The repeatable optical waveguideinterconnection of claim 1 further comprising a first ferrule mountingsaid first optical fiber, and a second ferrule mounting said secondoptical fiber.
 12. A repeatable optical fiber interconnectioncomprising: first and second optical fibers having respective first andsecond end faces, each of said first and second optical fiberscomprising a core having a core index of refraction, and a claddingsurrounding said core and having a cladding index of refraction lessthan the core index of refraction; and a first index matchingelastomeric solid layer having a proximal face chemically bound to thefirst end face and a low-tack distal face opposite the proximal face tobe repeatably optically and directly mechanically coupled to the secondend face, said first index matching elastomeric solid layer having anindex of refraction profile matching an index of refraction of said coreand said cladding; said first index matching elastomeric solid layercomprising an acrylate polymer.
 13. The repeatable optical fiberinterconnection of claim 12 wherein the low-tack distal face of saidfirst index matching elastomeric solid layer has surface propertiesdefining a wetted interface devoid of air pockets with said second endface when pressed thereagainst.
 14. The repeatable optical fiberinterconnection of claim 12 further comprising a second index matchingelastomeric solid layer having a proximal end face chemically bound tothe second end face and a low-tack distal face.
 15. The repeatableoptical fiber interconnection of claim 12 wherein said first end facehas a canted angle from perpendicular to an axis of said first opticalfiber; and wherein said first index matching elastomeric solid layer hasa uniform thickness and matches the canted angle.
 16. A method of makinga repeatable optical waveguide interconnection between first and secondoptical waveguides having respective first and second end faces, each ofthe first and second optical waveguides comprising a core having a coreindex of refraction and a cladding surrounding the core and having acladding index of refraction different than the core index ofrefraction, the method comprising: forming a first index matchingelastomeric solid layer having a proximal face coupled to the first endface and a distal face opposite the proximal face to be opticallycoupled to the second end face, the first index matching elastomericsolid layer having an index of refraction profile matching an index ofrefraction of the core and the cladding.
 17. The method of claim 16wherein the proximal end face is chemically bound to the first end face;and wherein the distal end face is low-tack.
 18. The method of claim 17wherein the low-tack distal face of the first index matching elastomericsolid layer has surface properties defining a wetted interface devoid ofair pockets with the second end face when pressed thereagainst.
 19. Themethod of claim 17 further comprising forming a second index matchingelastomeric solid layer having a proximal end face chemically bound tothe second end face and a low-tack distal face opposite the proximalface.
 20. The method of claim 16 wherein the first index matchingelastomeric solid layer comprises an acrylate polymer.